1. Field of the Invention
This invention relates to serial bus data transfer methods, and particularly to the transfer of isochronous data via an IEEE-1394 serial bus interface.
2. Description of the Related Art
Serial data busses are used in many applications. One use for such a bus is to convey digitized data from one device to another. For example, an analog audio signal might be digitized using an analog-to-digital converter (ADC) and then conveyed to a destination device via a serial data bus. Similarly, digitized audio data might be conveyed via a serial data bus and converted to one or more analog signals using respective digital-to-analog converters (DACs).
Some sort of interface circuit is typically required in such applications, interposed between the serial bus and the external devices providing or receiving the bus data, to process and format the data as needed by the external devices. One popular serial bus is compliant with the IEEE-1394 standard; products supporting this standard commonly use the trademarked name “FireWire”.
One typical application of an interface circuit which complies with IEEE-1394 is shown in FIG. 1. Here, the interface circuit is contained within an integrated circuit (IC) 10 known as an iceLynx-Micro® IC from Texas Instruments Incorporated. This IC includes first and second first-in/first-out (FIFO) memory devices (12, 14); FIFO 12 receives serial data from an IEEE-1394 bus 16, and FIFO 14 outputs data to the bus. IC 10 also includes an embedded processor 18 known as the ARM7DTMI® (“ARM”) which controls the timing of the IC, and a dual-banked shared memory 20, the use of which is application dependent.
In the example shown, serial bus 16 is used to convey digitized audio data. Data received from bus 16 is processed through FIFO 12 and provided to a DAC 22 via a serial bus such as an I2S bus 24; DAC 22 converts the digitized signal to one or more analog audio signals 26. Similarly, incoming analog audio signals 28 are digitized with an ADC 30, and conveyed back to bus 16 via an I2S bus 32 and FIFO 14.
However, there is a limit to the amount of data which can be conveyed by the system shown in FIG. 1. Because the iceLynx-Micro® IC was designed to handle either video or 5.1 channel audio data, the application shown in FIG. 1 can accommodate a maximum of six channels of audio data which has been sampled at a 192 kHz sampling rate. Unfortunately, for some applications, this data throughput limitation may be unacceptable.